This invention relates to a tool feeding device incorporating a signal controlling feed clutch which clutch is situated transmitting normal rotational forces to the tool feeding mechanism in its feed stroke, but which clutch automatically disengages and interrupts the tool feed stroke while simultaneously providing a signal usable for a coordinated control action upon the tool encountering abnormal resistance to its feed stroke movement. The abnormal resistance to the tool feed stroke may be created from various causes, for instance, a deliberately preset feed stroke limiting stop intended to determine the length of the feed stroke, or an unforeseen obstruction encountered by the tool and spindle at any location during the feed stroke, or even a prohibitively dulling tool becoming incapable of properly carrying out a cutting or drilling intended function. Furthermore, the signal created by the clutch disengagement may be used for various coordinated control purposes such as automatically through cooperable mechanism reversing the tool spindle feed stroke and at least permitting a commencement of and carrying out the tool spindle retraction stroke.
Tools of the type herein involved have previously been provided with feeding mechanisms incorporating clutches for protecting both the feeding mechanism and the tool and spindle upon the tool or spindle encountering an unforeseen obstruction during the feed stroke. For instance, such a prior tool may incorporate a drive motor operably connected providing rotational motion to the tool spindle and tool, and also operably connected providing rotational motion through an overload clutch to a lead screw and nut arrangement. The spindle is arranged for axial movement during rotation thereof in feed and reverse retraction strokes, and the lead screw is connected independently rotatable relative to the spindle but capable of carrying the spindle axially in its feed stroke. Thus, at the commencement of a spindle feed stroke, the lead screw is engaged by the nuts and rotation of the lead screw relative to the nuts drives the independently rotating spindle in its feed stroke, after which, the nuts are released from the lead screw and the spindle may be returned in its retraction stroke merely through spring urging or any other appropriate retraction stroke force.
In these prior tool feeding devices, control of the lead screw and nut engagement and disengagement has been accomplished through movable cams actionable against the nuts through exteriorly accessible control sleeves and the like. With the spindle retracted and ready for the feed stroke, the exterior sleeve is manually manipulated to actuate the cams moving the nuts into engagement with the lead screw commencing and ultimately carrying out the intended spindle feed stroke. Upon completion of the intended spindle feed stroke, engagement of the spindle with a preset stop arrangement operably connected to the sleeve causes the cams to release the nuts into disengagement from the lead screw thereby permitting the following spindle retraction stroke.
The sole purpose of the overload clutch in the rotatable connection between the drive motor and the feeding lead screw is to provide overload protection for the spindle and tool during the feed stroke in the event either should encounter an unforeseen obstruction. Furthermore, the entire reaction of this overload clutch in its protection function is to temporarily interrupt further axial feeding motion being transmitted through the lead screw to the spindle and tool. In other words, upon the spindle or tool meeting an unforeseen obstruction during the feed stroke, an abnormal resistance to further feed stroke movement created by the obstruction is transmitted reversely through the lead screw and into the overload clutch causing actuation of the clutch to temporarily discontinue the transmission of rotational motion therethrough to the lead screw.
During maintainment of such unforeseen obstruction, the spindle and tool will continue to rotate through their independent connection to the drive motor, but the obstruction will retain the formerly rotating lead screw stationary as permitted by the disconnection of the clutch and the interruption of rotational motion to the lead screw from the drive motor. As soon as the obstruction is removed, thereby removing the abnormal resistance to feed stroke movement and removing the transmission of such resistance back through the lead screw and to the disengaged clutch, the then disengaged overload clutch will immediately re-engage properly transmitting rotational motion therethrough from the drive motor to the lead screw so as to resume normal functioning of the lead screw and the normal axial feeding motion of the spindle and tool. It is evident, therefore, that the sole function and the sole capabilities of the clutch in these prior tool feeding devices is the described overload protection function in most cases guarding the spindle and tool, as well as possibly the lead screw and nut feeding mechanism, against damage from the unexpected obstruction.
Obviously, with this type of clutch having solely the overload protecting capabilities as described, such clutch is independent of and completely isolated in the functioning sense from the remainder of the particular tool feeding device including any control mechanisms of the particular tool feeding device. For instance, if a workman is not immediately present to remove the unexpected obstruction or shut down operation of the tool feeding device when such obstruction is encountered by the spindle or tool and the clutch is actuated to disengaged position, the spindle and tool will continue to rotate without further axial feed motion and the clutch will remain disengaged. This condition will persist until positive action is taken by the worker. Furthermore, there are many occasions where it is either impossible to immediately find the obstruction or impossible to readily remove the same resulting in still further positive action being required by the workman to remove the tool or spindle from such obstruction prior to resumption of normal tool feeding device function, thereby increasing the work stoppage delays and adding further to the difficulties involved.